Bet Builder: Parlay and Forecast Calculator
A bet builder multiplies your selections into one price and shows the return, the profit and the chance you need to break even. Enter odds in American, decimal or fractional form and the tool works out the rest.
Key takeaways
- A parlay multiplies the decimal odds of every leg, so three legs at -110, +150 and -200 combine to 7.159 decimal, or +616 American.
- Four legs at -110 pay 13.28x where fair odds would pay 16x, so the extra legs cost you 17% of the fair payout.
- A forecast bet picks the first and second place in order, and a reverse forecast covers both orders for two stakes.
- The forecast price here is a Harville estimate from your win odds, so use it as a fair price to compare against, not as a quote.
- The break-even chance is one divided by the combined decimal odds, and a parlay needs every leg to win.
On this page
- Bet Builder Calculator
- How Do You Calculate Parlay Odds?
- How Do American, Decimal and Fractional Odds Compare?
- How Much Do Extra Legs Cost?
- What Is a Forecast Bet?
- How Is the Forecast Price Estimated?
- Why Does the Real Forecast Dividend Differ?
- Are Parlays Worth Betting Compared With Singles?
- Bet Builder FAQs
Bet Builder Calculator
Choose a parlay or a forecast, pick the odds format you use, and enter your stake and selections. The tool returns the combined odds, the return and the chance you need to break even.
| Legs priced | 3 |
|---|---|
| Combined decimal odds | 7.159 |
| Combined American odds | +616 |
| Combined fractional odds | 6.16/1 |
| Total return if every leg wins | 71.59 |
| Profit if every leg wins | 61.59 |
| Break-even chance of all legs winning | 13.97% |
A parlay multiplies the decimal odds of each leg, so the margin in every price multiplies as well. Every leg must win, and one loss loses the whole stake.
The parlay mode takes two to twelve legs. The forecast mode takes the win odds of two selections and estimates the price of finishing first and second in order.
How Do You Calculate Parlay Odds?
You calculate parlay odds by converting every leg to decimal odds and multiplying them together. The product is the combined decimal price, and your stake times that price is the total return.
Take three legs at -110, +150 and -200. Those are 1.909, 2.500 and 1.500 in decimal, and they multiply to 7.159, which is +616 in American odds. A $10 stake returns $71.59, which is $61.59 of profit.
A single lost leg ends the bet. That is why the break-even chance is one divided by the combined price, which here is 13.97%.
How Do American, Decimal and Fractional Odds Compare?
The three formats describe the same price, and the implied probability is one divided by the decimal odds. The table converts common prices.
| American | Decimal | Fractional | Implied chance |
|---|---|---|---|
| -200 | 1.500 | 1/2 | 66.67% |
| -150 | 1.667 | 2/3 | 60.00% |
| -110 | 1.909 | 10/11 | 52.38% |
| +100 | 2.000 | 1/1 | 50.00% |
| +150 | 2.500 | 3/2 | 40.00% |
| +250 | 3.500 | 5/2 | 28.57% |
| +500 | 6.000 | 5/1 | 16.67% |
To convert American odds to decimal, divide a positive price by 100 and add 1, or divide 100 by a negative price without its sign and add 1. Fractional odds are the decimal price minus 1, written as a fraction.
How Much Do Extra Legs Cost?
Each extra leg takes a larger share of the fair payout, because the margin in every price multiplies. The table prices legs that each sit at -110, where a fair price would be 2.000 per leg.
| Legs | Combined decimal | American | Break-even chance | Share of fair payout lost |
|---|---|---|---|---|
| 2 | 3.645 | +264 | 27.44% | 8.9% |
| 3 | 6.958 | +596 | 14.37% | 13.0% |
| 4 | 13.283 | +1228 | 7.53% | 17.0% |
| 5 | 25.359 | +2436 | 3.94% | 20.8% |
| 6 | 48.413 | +4741 | 2.07% | 24.4% |
Four legs at -110 pay 13.28 where fair odds would pay 16. That is a 17.0% shortfall on one bet, against a shortfall of about 4.5% on a single -110 bet.
What Is a Forecast Bet?
A forecast bet asks you to pick the first and second finishers of an event, in the right order. It is common in horse and greyhound racing, and it pays more than backing each selection to win because you need both to be correct.
A straight forecast needs your first pick to win and your second pick to finish second. A reverse forecast covers both orders, so either pick can win and the other must be second.
A reverse forecast costs two stakes, one for each order. Only one of them can win, so the cost per order is the same as the straight bet.
How Is the Forecast Price Estimated?
The tool estimates the chance of a forecast with the Harville model. It takes each pick's win chance, then asks how likely the second pick is to win among the remaining runners.
The chance of A first and B second is the win chance of A times the win chance of B divided by one minus the win chance of A. The win chances come from your odds after the bookmaker margin is removed.
| Market margin | Bet | Estimated chance | Fair decimal odds |
|---|---|---|---|
| 0% | Straight forecast, A 3.00 and B 4.00 | 12.50% | 8.00 |
| 0% | Reverse forecast | 23.61% | 4.24 |
| 15% | Straight forecast, A 3.00 and B 4.00 | 8.87% | 11.27 |
| 15% | Reverse forecast | 16.92% | 5.91 |
A bigger margin lowers each pick's true chance, so the fair price for the forecast rises. Enter the margin of the market you are looking at, or 0 if you only want the odds as quoted.
Why Does the Real Forecast Dividend Differ?
The real forecast dividend differs because a pool or the bookmaker sets it, not a formula on your odds. A pool pays what the money bet on each combination dictates, and bookmakers commonly settle a forecast from the final prices with their own computer calculation.
Use the estimate as a fair price to compare against. If a dividend or quote is well below it, the margin in that bet is large.
Are Parlays Worth Betting Compared With Singles?
Parlays carry a higher margin than the same bets placed as singles, because the margin multiplies across legs. A parlay is a reasonable choice for a small stake when the payout is the point, and a poor one when you want to keep your costs low.
Our hold and no-vig calculators show the margin in a pair of prices, and the parlay margin calculator shows how it compounds across legs.
Hold and no-vig calculator · All calculators · Bankroll calculator
Bet Builder FAQs
How do you calculate a parlay payout?
Multiply the decimal odds of every leg, then multiply by your stake. A $10 stake at combined decimal odds of 7.159 returns $71.59.
How do you convert American odds to decimal?
For a positive price, divide by 100 and add 1. For a negative price, divide 100 by the price without its sign and add 1, so -110 becomes 1.909.
Can you mix American and decimal odds in one parlay?
Convert every leg to one format first. The tool prices one format at a time, and you can switch the format to see each price in the others.
What is a reverse forecast bet?
A reverse forecast covers both finishing orders of your two picks, so it costs two stakes. It wins if either pick is first and the other is second.
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